Molded plastic solar still

ABSTRACT

A dimensionally rigid solar distillation apparatus for vaporization and condensation of water, including a slanting transparent sheet supported on generally upright wall members extending from a generally flat base wherein the wall members and base are formed from pressure molded, foamed plastic material.

United States Patent Hensley, Jr. et al.

[15] 3,655,517 [451 Apr. 11, 1972 [54] MOLDED PLASTIC SOLAR STILL [72]Inventors: Justin C. Hensley, Jr., 4464 Davenport Ave., Oakland, Calif.94619; Paul G. Young, 6500 Buena Ventura Ave., Oakland, Calif. 94605Filed: Oct. 22, 1969 Appl. No.: 868,478

US. Cl. ..202/234, 203/D1G. 1 Int. Cl ..B0ld 3/00 Field of Search..202/234, 173, 236, 205;

203/10, 100, 72, DIG. 1; 159/1 S References Cited UNITED STATES PATENTS2,614,973 10/1952 Burrows ..203/72 X 2,848,389 8/1958 Bjorksten......202/234 2,877,164 3/1959 Meyer ..202/185 Lappala et al. ..202/234Mount ..202/ 234 3,282,327 11/1966 Hardy et al. "159/1 S 3,290,23012/1966 Kobayashi ....202/234 3,290,231 12/1966 Ries et al. ..203/103,336,206 8/1967 Sasaki et al. ..203/10 X 3,351,538 11/1967 Andrassy..159/1 S 2,446,997 8/1948 Brewer et al ..202/205 X PrimaryExaminer-Norman Yudkofi Assistant Examiner-J. Soffer Attorney-Townsendand Townsend [5 7] ABSTRACT A dimensionally rigid solar distillationapparatus for vaporization and condensation of water, including aslanting transparent sheet supported on generally upright wall membersextending from a generally flat base wherein the wall members and baseare formed from pressure molded, foamed plastic material.

5 Claims, 4 Drawing Figures GRID-LIKE MAT-2|"1 llllllllllj .directedmainlytothqproduction of potablewater from saline -.water but wider;application is anticipated and is implied.

Theart of producing potable water from brackish water or seavwaterbymeans of solar distillationis well known and is .quitesuitableforruraldomestic use or for small villages, particularly in.coastal areas. SeveraLdesigns of solar stillsare .knownincludingrectangular andround based horizontal stills and .tilted ,tray stills.Conventional materials of construction are wood, plastic, metal orconcrete (frames supporting a slanted glass or transparentplastic coversheetover a pool or poolsof the brine; the'transparent sheet allows.radiant heat to pass ,throughit andthusenter the still and to provideheat to vaporize athedistilland. Vapor thus produced condenses oncontact withthe lower side of :the sloping transparent sheet thatiscooledbythe. atmospheric air outsidethe still. Heat ofcondensationof-the vapor is thus passed to the atmospherethrough.the=transparent sheet, and the condensate adhering to the lowerside of the sloping sheet is collected by gravityflow and ispiped outofthe still for, use. The distilland consisting of brackish .water isreplenished either intermittently or by constant flow throughthe basearea of the still. Solarenergy is thus captured .in the still, isutilized to provide heat of vaporization \of unpotable water .and ispassed to the atmosphere;uponcondensation of the vapor into potabledistillate water. Thedriving force, solar. heat, is free but theeconomy. andproductivity of a solar still canbe greatly enhanced byimproved thermal efficiency and by. reducing the cost of constructionand of materials. This specification provides for such improvements overthe prior art.

'51 he thermal efficiency of a solar still is greatly improved-by.thisinvention comprising the use of'moldable foamed plastics,

:particularly expanded. foamed plastics; for instance, expandedpolystyrene,- or a similar. material, having superior heat insulatingproperties; and this represents a major advantage over the .priorart.The structuralstrength of such molded forms and the light weight of suchmaterials provide for improved materials economy, and the, ease ofmanufacturing and the low unit cost. of molding amultiplicity ofthe'required frames or shapes constitute substantial improvements overthe prior art.

DESCRIPTION OF FIGURES .FIG. I is a perspective side view section of apreferred form ofthe Molded PlasticSolar Still.

fl-1G. II is a side view section of a Molded Plastic Solar Still.

.EIG. Ill,i s a side view section of a Molded Plastic Solar Still 1foruse.on damp ,soil or;for placing over damp material containingadistilland. 1

'EIGJlVjS a side view section of a generally rectangular Molded PlasticSolar Still that is tilted when in operation.

ZDESCRIPTION'OF PREFERRED EMBODIMENTS Thetrateof distillate.productionof a solar still depends mainlyupon therateof absorption of solar heat,the dif- .ference. in temperature between the'surface of the .brine*heatedby solar, radiation and the condensing surface, and the surface,areas, at which mass or heat transfer takes place. Since the .solar,heat received for a given location and shape and size of solar .still isfixed, the productivity rate can be enhanced mostsignificantly byreducing thermal losses so thata maximum of the captured heat is usedfor evaporation and is passed to the atmosphere by condensation of thevapor on the lower side of the air-cooled transparent sheet. A majoradvantage of, the still of .this invention is that it provides forexcellent heat insulationto reduce then'nal losses to a minimum. Infact, it has been found that the productivity rate of the preferredsolar still of this specification exceeds that of comparable solarstills of conventional construction and materials by-60to percentwhentested simultaneously under equal operating conditions. Thematerials of construction as conceived in this invention, vizfoarnedplastichaving high thermal insulating properties, constitutes asignificant improvement overthe prior art. A second significantimprovement over the prior. art results'from the mode of construction,viz by moulding the-framefor supporting the transparent sheet. Forinstance, the cost of materials and of construction of a unit of .thepreferred solar still of this specification can be less than half vthecost-of a comparable still of conventional materials and constructionwhen both are produced in quantities in excess of 500.

The shape and size of the molded plastic solar still of thisspecification are not confined to the preferred embodiments shownanddescribechthis material and method of construction can be utilized inunlimited shapes and sizes. The mode of construction and materials ofconstruction of this specification are, applicable to all forms of solarstills known in the art.

vThe lightweight material used for construction, readily adaptable tomass production bymolding, and the dimensional rigidity of themoldedform of this material, and the capability of being made in units ormodules of any desired shape and size represent a major advance in theart.

The unitized mode of construction of this specification readily allowsfor the replacement of defective units in a multiunit solar stillwithout interrupting the operation of remaining units.

.When the bottom (base) of thestill is omitted, it can be used toproduce potable water from vapors released from damp materials, forinstance by placing the frame on the ground. This can be of vitalimportance-under. desert conditions-Similarly, potable water can beproduced from vegetable matter oranother source. of dampness, forexample, from mud or moist earth, especially at night when heat storedin the earthproduced vapor that condenses readily on the cover glassthat is in contact with the cool night air, a condition somewhatcomparable to dew formation. In addition, a perplane.

The following is a description of the preferred embodiments of thisinvention and of their operation, with reference to the FIGS.

FIG. 1 shows a perspective section view of a molded foamed plastic solarstill comprising a rectangular-based molded frame-having generallyvertical sides 1 supporting a slanted glass cover 2 for transmittingsolar radiation into the body of the still. The top edge of the moldedside walls of the still are shaped to receive the glass cover 2, forinstance standard window pane of suitable dimensions, and to form a goodseal therewith. This seal may be improved by applying any suitableglazing compound or sealant to seal or secure the glass 2 to theframe 1. The inclination or slant of the cover glass 2 is such as toallow passage of a maximum of solar radiation and to permit condensateto collect and drain from it as a thin film in contact with the lower(inside) surface of the cover glass 2. This condensate is collected in ahorizontal trough 3 that may be molded into the base frame 1 along itslower side wall but being separated from the main liquid reservoir 4 inthe still, for instance, by a suitable molded divider wall having a topedge spaced from the cover glass 2. Condensates collected in the trough3 can be removed from the still by means of a suitable conduit, forinstance, a pipe 5 communicating with the trough and extending throughthe wall of the still. The main liquid reservoir 4 can be molded as anintegral part of the frame and provides for a shallow pool of distillandthat can be replenished as required, for instance, through an inletconduit 6 at the back side of FIG. 1. A similar outlet conduit located adistance from the inlet conduit 6 may be provided to allow continuous orintermittent drainage of concentrated residual distilland from thestill.

FIG. 11 shows a side view section of a molded plastic solar still, thebase and sides 7 of which are made preferably from expanded or foamedplastic, for instance, expanded polystyrene, polyurethane or anothersuitable moldable material having good thermal insulatingcharacteristics. A transparent cover sheet, for instance, glass ofwindow pane type 8, fits over or on the sides or into a slot ordepression 9 formed by molding so as to provide a good fit between theglass surface and the body (sides) of the still. A trough 10 forcollecting the condensate and a conduit 11 to communicate with thetrough 10 to allow withdrawal of the product from the i still can beprovided by molding. The main base area 12 of the still provides areservoir for the distilland and an area for collecting solar heat toeffect vaporization of the distilland. The base area 12 shouldpreferably be of a dark or black color to enhance absorption of solar orradiant heat. Alternatively, this inside surface may be painted with adark material, or a dark surfaced material, for instance, a sheet of tarpaper 13 or a layer of dirt or dark sand may be placed in the base toincrease the rate of absorption of solar heat. A rough surface is alsohelpful. For example, small stones 14 can be placed in the base area oron the tar paper to hold it down while at the same time providingadditional heat transfer surface area, and for dissipation of heat tothe distilland by creating convection currents in the layer ofdistilland close to these surfaces. Altematively, a rough surfacepattern and/or a dark surface can be provided by molding or by a placinga preformed grid or mat on the base 12. The distilland can bereplenished intermittently as needed, or continuously for instance by bypassing it into the base area of the still through a suitable conduit15. Residual distilland or brine can be withdrawn or can overflow fromthe still through a suitable conduit 16. A sealant may used to improvethe seal formed between the cover glass 8 and the body 7 of the still orone can rely on a liquid seal provided by the condensate filling the gapbetween these surfaces. The inclination of the transparent sheet orcover glass 8 is sufficient to ensure that the condensates collected onits lower (inside) surface drains towards the collection trough 10 andto provide for a maximum transmission of solar heat into the still. FIG.111 shows a side view section of a molded plastic solar still that hasan open base. This provides that it may be placed on damp soil or overanother suitable source of moisture, for instance, plant material fromwhich potable water may be obtained by vaporization and by condensationof the vapor. A condensate collection trough 17 having an outlet conduitconnected therewith can be molded into one side of the still and thetransparent cover sheet or glass plate 18 may be sealed to the uppersurface of the molded sides 19. A detachable base 20 of any suitablematerial, shape or size, for instance molded plastic, may be provided.Provision is also made for placing a sponge or gridlike mat 21 or othersuitable wetable material to hold water while it is being partiallyvaporized, for instance, when the solar still is used on shipboard, asponge-like insert as a precaution against sloshing of the distilland isof importance. Sloshing of condensate in the trough 17 may be preventedsimilarly by placing a sponge-like material in it.

FIG. IV shows a side view section of a molded plastic solar still thatis supported in a tilted orientation at a suitable angle duringoperation. One advantage of the tilted tray still is that the vapor pathof flow from the distilland surface to the condensate surface is short.Another is that the material required for the wall structure to supporta unit surface of glass is reduced as compared to other types of solarstills. The tilted tray still also allows for increased evaporatingsurface area and for a reduction of shading of the base surface area bythe side walls of the still, thus increasing the radiant heat absorptionat this surface and enhancing the evaporation rate of the distilland. Inthe preferred embodiment of the molded foamed plastic solar still of thetilted tray type shown, the side walls 22 are relatively low, thusproviding for the relatively close proximity of the evaporating surfaceand the condensing surface, for instance, a gap of about one-half inchbetween these surfaces is adequate in most cases. The base 23 can havean integrally molded saw-tooth pattern 24 on its inside surface so as toprovide for parallel troughs or pools of distilland and for cascading ofthe distilland under gravity flow from one trough to the next.Altemately, a zig-zag flow path can be provided for by arranging thedistilland inflow and outflow for successive troughs to be at oppositeends thereof through the series of troughs. This provides for anelongated, zig-zag flow path of the distilland through each still and itenhances the evaporating coefficient or rate. The cover glass 25 oranother suitable heat-transparent sheet can be supported loosely on ashoulder provided by molding the top edge of the side walls 22. Adistillate or condensate collecting trough 26 can be provided by moldingit into the side wall as shown. Distilland inlet 27 and outlet 28conduits and a condensate outlet 29 can be provided by molding suitableholes and by inserting suitable tubular conduits as shown, for instance,short lengths of plastic pipe inserted through the side walls 22 atsuitable locations. A suitable sea] at 30 between the cover glass 25 andthe side walls 22 may be obtained by proper molding and by relying on aliquid seal provided by condensate seeping into and sealing the gap at30 or it may be obtained by applying a glazing compound, a plasticsealant, glue or by sticky tape applied over or in the joint at 30.

Additional shapes, sizes or modules of molded foamed plastic solarstills or sectional parts thereof can be utilized singly or in multipleseries operation without departing from this specification; forinstance, rounded rather than angular shapes and pre-molded sectionsfitted or joined together. In addition, the separate uses or functionsof vaporization and condensations according to this invention areanticipated and covered by this specification. The embodiments shown andthe applications described are intended as examples and this inventionis not to be limited to or by these examples. For instance, these sameprinciples can be utilized to heat water, to make or recover salt frombrine, to produce distilled water for medical or pharmaceutical orphotographic or industrial or domestic uses, for instance, for batteriesand steam irons. Different types of foamed or foamable plastic materialscan be used, for instance, polyurethane, polystyrene, styrofoam,pelafoam, etc. and different modes of molding can be utilized to producecomponents of the molded, foamed plastic solar still without departingfrom the scope of this specification.

The invention claimed is:

l. A dimensionally rigid solar distillation apparatus including a framecomprising a generally flat base and a plurality of generally uprightwall members extending upwardly for a short distince and completelyaround the entire periphery of said base, an enclosing, bottomless andtopless housing comprising a similar plurality of upright wall membersof equal number but greater height than those of the base and slopingfrom its highest to its lowest opposite wall, said housing seating onthe base within its relatively short upright wall members, said lowestopposite wall having a channel in its upper edge for collectingcondensate drippings from the cover sheet, a slanted transparent coversheet capable of transmitting radiant heat and providing an innersurface for condensation of evaporated liquid, said sheet being spacedfrom said base by said upright members of said housing to provide achamber adapted to retain a body of vaporizable, brackish water indirect connect with the base and wall members of said frame, conduitmeans in said frame for introducing and removing brackish water andrecovering liquid condensate, said apparatus consisting essentially ofmolded, foamed plastic material and said base having means disposedthereon for preventing sloshing of the liquid within said frame.

tilted orientation at a suitable angle.

4. Apparatus as in claim 1, further including provision for placing apreformed gridlike mat within said frame to enhance the rate of heattransfer to said distilland and to prevent sloshing of liquid withinsaid frame.

5. Apparatus in accordance with claim 1 wherein said foamed plasticmaterial is selected from expanded polyurethane and polystyrene.

1. A dimensionally rigid solar distillation apparatus including a framecomprising a generally flat base and a plurality of generally uprightwall members extending upwardly for a short distince and completelyaround the entire periphery of said base, an enclosing, bottomless andtopless housing comprising a similar plurality of upright wall membersof equal number but greater height than those of the base and slopingfrom its highest to its lowest opposite wall, said housing seating onthe base within its relatively short upright wall members, said lowestopposite wall having a channel in its upper edge for collectingcondensate drippings from the cover sheet, a slanted transparent coversheet capable of transmitting radiant heat and providing an innersurface for condensation of evaporated liquid, said sheet being spacedfrom said base by said upright members of said housing to provide achamber adapted to retain a body of vaporizable, brackish water indirect connect with the base and wall members of said frame, conduitmeans in said frame for introducing and removing brackish water andrecovering liquid condensate, said apparatus consisting essentially ofmolded, foamed plastic material and said base having means disposedthereon for preventing sloshing of the liquid within said frame. 2.Apparatus as in claim 1 wherein said means on said base comprisessponge-like means to prevent sloshing of said liquid with said frame. 3.Apparatus as in claim 1, wherein said molded foamed plastic baseprovides a multiplicity of parallel distilland pools within said frame,the water containing portion of said base being generally parallel tosaid sheet for transmitting radient heat and spaced therefrom by about 1inch, said base having a saw-tooth profile that provides for saidparallel pools of distilland in series flow connection by supporting theapparatus in a tilted orientation at a suitable angle.
 4. Apparatus asin claim 1, further including provision for placing a preformed gridlikemat within said frame to enhance the rate of heat transfer to saiddistilland and to prevent sloshing of liquid within said frame. 5.Apparatus in accordance with claim 1 wherein said foamed plasticmaterial is selected from expanded polyurethane and polystyrene.